The present invention relates to the field of information storage and retrieval using integrated circuit technology. More specifically, the present invention relates to techniques for storing (and retrieving) analog or digital data, or both, within an integrated circuit using multilevel nonvolatile cells.
Among the most important and pioneering innovations in history are devices, techniques, and mediums that have been devised to record and playback sights, sounds, actions, and other information. Many of these innovations have led to the rise and growth of the media and entertainment industries, and also the personal and consumer electronics industries.
For example, among the most notable inventions are Thomas Alva Edison's phonograph and record with which Edison recorded and played his first recording “Mary Had a Little Lamb.” Other achievements in this field are the audio tape recorder, cassette tape recorder, motion picture, talking motion picture (“talkies”), video cassette recorder (VCR), compact disc (CD and CD-ROM), video disc, digital video disc (DVD), and many, many more of such innovations. In the present day, full-length motion pictures with stereo sound may be contained on a single optical disk.
Although these technologies have met with substantial success there is a continuing desire to improve on the techniques, devices, mediums used to record information. For example, there is a need to provide techniques that provide dense storage of information. Denser storage facilitates storing information in a compact area, and provides a relatively long recording time.
There is a need to provide reliable and robust techniques. The stored reproduction should be a faithful reproduction of the original information. Despite repeated use, the stored reproduction should retain its original form, and also not degrade over time. Furthermore, the techniques should be compatible with and interface easily with present and emerging technologies in electronics and with devices facilitating electronic commerce (such as the Internet and World Wide Web).
Integrated circuit technology has been used to implement many electronic devices including computers, video recorders, digital cameras, microprocessors, DRAMs, SRAMs, Flash memory, and many others. As integrated technology continues to improve, it becomes practical to use this technology to record and playback sights, sounds, actions, and other information.
Data has typically been stored within integrated circuits using a digital or binary format. For applications where the input is analog, however, this requires conversion of signals to digital format, generally by an analog-to-digital (A/D) converter or similar means. And playback of analog signal from a digital storage format may require a digital-to-analog (D/A) converter or similar means. As can be appreciated, these conversions add complexity and extra expense to the entire procedure. Further, a conversion of the signal to digital form quantizes the signal and will lead to quantization noise in the reproduced signal.
Information such as sounds and voices, stereo and multichannel sounds, pictures, video, and others requires many bits of data storage. Storage of data in digital format may be inefficient because one bit (i.e., two different levels) of data is stored in a single memory cell. Further, it may be desirable to store an input signal using a sampling rate the user selects.
Therefore, techniques are needed for compactly storing (and retrieving) analog and digital information including sights, sounds, and actions using integrated circuit technology.